The present invention relates to an immersion nozzle to be used for pouring molten steel in continuous casting of steel.
The immersion nozzle usually has two delivery ports formed in the left and right at around a lower end of a nozzle bore thereof. Because flow rate control is carried out by reducing the nozzle-bore area, such as in a sliding plate or upper nozzle during casting, the immersion nozzle has an inner diameter of nearly 1.1 to 3 times the reduced-bore area. Due to this, there is a tendency that the molten steel falling from the plate or upper nozzle deviates in its flow center, to cause flow deviation such that the molten-steel flow through the nozzle bore deviates to one side. As a result, there are cases that molten steel does not flow out equivalently in the left and right through the delivery ports. The deviation at the delivery ports prevents molten steel from homogeneously solidifying within a mold, resulting in an uneven structure in the solidified cast piece.
FIG. 17 is an example of a device for flow-rate control by sliding a middle plate 81 of a sliding plate device 80 comprising three plates, wherein the sliding direction is perpendicular to the delivery port 82. In this example, although the molten steel flow deviates as indicated by the arrow, it is used with the intention that, because the direction of deviated flow is in perpendicular direction to the delivery port 82, the delivery flow at the nozzle delivery port might be free from deviation. However, actually deviation occurs also in the delivery flow at the delivery port. The cause of this is considered to be that because the flow deviation caused by sliding the hole of the middle plate 81 could be twisted during falling through the nozzle bore 83, deviation would be caused in the delivery flow at the delivery port 82.
Meanwhile, Japanese Patent Laid-Open Publication No. 11-123509 describes that the provision of a step structure in an immersion-nozzle bore makes it possible to prevent the immersion nozzle from being clogged due to alumina deposition and further flow deviation in the immersion-nozzle bore from occurring thus making the in-pipe flow velocity even.
However, according to the test repeated with water model experiments by the present inventors, it has been found that a step does not completely prevent against flow deviation in the delivery flow resulting from flow deviation through the immersion-nozzle bore caused by a sliding nozzle, stopper or the like for controlling the flow rate of molten metal from the tundish to the immersion nozzle.
The present invention is, in an immersion nozzle to be used for steel continuous casting, a flow-deviation preventing immersion nozzle, shown in the following (1) to (6) descriptions, for preventing flow deviation in a delivery flow resulting from the flow deviation in the bore region.
(1) A flow-deviation preventing immersion nozzle as an immersion nozzle having opposite two delivery ports has one or more bore reduced portions at above the delivery port in a bore, wherein the bore reduced portion closest to the delivery port is an elliptic bore reduced portion having a bore form of an ellipse in horizontal section, and an elongate direction of the ellipse is nearly parallel with a direction of the delivery port.
(2) A flow-deviation preventing immersion nozzle according to (1), wherein a bore elliptic reduced portion having an ellipse having an elongate direction nearly parallel with the direction of the delivery port is provided as a bore reduced portion second closest to the delivery port.
(3) A flow-deviation preventing immersion nozzle according to (1) or (2), wherein the uppermost bore reduced portion is a bore elliptic reduced portion having an ellipse in a direction perpendicular to a slide direction of a plate.
(4) A flow-deviation preventing immersion nozzle according to (1), (2) or (3), wherein the bore in other than the bore reduced portions is nearly circular in section thereof.
(5) A flow-deviation preventing immersion nozzle according to (1), (2), (3) or (4), wherein a lower end surface of the bore elliptic reduced portion closest to the delivery port is 0.3H-2H of a delivery port height H of from an upper end of the delivery port.
(6) A flow-deviation preventing immersion nozzle according to (1), (2), (3) or (4), wherein a lower end surface of the bore elliptic reduced portion closest to the delivery port is 0.3H-2H of a delivery port height H of from an upper end of the delivery port, the spacing to the upper bore elliptic reduced portion being 0.3D-2D of a diameter D of the bore, and moreover a length of each bore reduced portion being 0.5D-5D.